Support towers for communication equipment have in the past conventionally been of lattice-type construction. In such construction, the towers are provided with a relatively broad base, typically having a rectangular cross-section, which narrows significantly towards the top of the tower. Much cross-bracing is used in the tower, and the overriding design criteria for such towers has been to erect the tallest tower with the least amount of steel. This provides a relatively inexpensive structure, but one which requires a significant amount of labour to erect.
In the past, such towers have been used primarily for microwave dishes. Such dishes would be mounted either on a leg or on a tower face. However, such mounting substantially increases the wind load of the structure and thus additional steel may be required to be used in the design. If a pre-existing tower is to be modified to support an additional dish, the addition of any reinforcement can be difficult and awkward.
Recently, however, the development of the cellular telephone network, through use of a multiplicity of cellular antennas, has changed the requirements of the support towers. Typically, cellular antennas require a horizontal separation of 12-15 feet to achieve the desired receiver diversity. On a conventional tower, with an upward taper to a point, the only way to achieve the desired separation is to add long boom mounts to the tower. The addition of long boom mounts greatly effects the wind-loading and adds to the busy appearance of an already busy lattice structure. Indeed, the requirement of the addition of cellular antennas together with the long boom mounts may exceed the design loading of conventional towers and require the retro-fitting of additional cross-bracing up the length of the tower. This additional bracing further increases the busy appearance of the structure and adds to the expense of installation of the antennas.
What is desired is a new support tower structure, which is simple and easy to erect, and which provides the required degree of separation at the top without the need for overhanging boom mounts. What is also desired, is a support tower, which provides a range of azimuths for mounting microwave antennas, but which retains the antenna close to the tower structure and even partially recessed within the tower for lower wind loading, easy adjustment and the like.